CN102494742B - Method for on-line calibration of large-caliber flow meter - Google Patents

Abstract

A method for on-line calibration of a large-caliber flow meter comprises four steps: step one is selection of a standard flow meter; step two is design of a bypass pipeline; step three is installation of a standard meter; and step four is evaluation of method performance. The method for the on-line calibration of the large-caliber flow meter is based on a calibration principle of a standard meter method, and adopts a turbine flow meter with high precision to serve as a standard meter to achieve calibration of the large-caliber flow meter. Based on the consideration of range of the turbine flow meter, the bypass pipeline is led out at the upper stream or the lower stream of the large-caliber flow meter, and the standard flow meter is installed in the pipeline. Then when fluid passes by the flow meter, a flow value of the standard flow meter is recorded, and calibration of the large-caliber flow meter is achieved according to the mathematical functional relation between the measurement result of the flow of the bypass pipeline and the large-caliber flow meter of a main pipeline. The method for the on-line calibration of the large-caliber flow meter has novel conception, accurate calibration and practical value and wide application prospect in the technical field of flow meter detection.

Description

A kind of method of heavy caliber flowing meter on-line calibration

Technical field

The present invention relates to a kind of method of heavy caliber flowing meter on-line calibration, belong to flowmeter detection technique field.

Background technology

Development along with urbanization, the increase of water consumption and discharge capacity, the demand of heavy caliber flowing meter constantly increases, and dispatch from the factory at eservoir diversion, source water water inlet factory, tap water, the fields such as wastewater treatment and sewage discharge are used widely, but correspondingly, flowmeter uses the rear precision problem that faces also to become increasingly conspicuous long-term.

The heavy caliber flowing meter that uses both at home and abroad at present comprises electromagnetic flowmeter, ultrasonic flowmeter, orifice flowmeter etc.Wherein electromagnetic flowmeter is a kind of Ferraris instrument that comes conducting medium volumetric flow rate in the measuring tube according to Faraday's electromagnetic induction law, its precision can reach (0.2～0.5) %, ultrasonic flow meter is as principle take " velocity contrast method ", measure the instrument of fluid flow in the pipe, its precision is 0.5%, and orifice flowmeter is comprised of throttling element and differential pressure gauge, when the restriction device of the flow that is full of pipeline in pipeline, near throttling element, cause local contraction, flow velocity increases, by on it, it is poor that the both sides, downstream produce static pressure, can derive relation between differential pressure and the flow according to the Bernoulli equation in the fluid mechanics, thereby can try to achieve the flow value of fluid, its precision is 1%～2%.For the especially bigbore orifice flowmeter of orifice flowmeter, because its precision is relatively low, and is subjected to the impact of mounting condition and service condition larger, therefore in the large diameter pipeline flow measurement, use less.For electromagnetic flowmeter, because its measuring accuracy is relatively high, and ultrasonic flowmeter has characteristics easy for installation, so these two kinds of flowmeters are widely used in the large diameter pipeline flow rate test.These heavy caliber flowing meters can face the problem of accuracy calibration after long-term the use, for electromagnetic flowmeter, be the highest a kind of flowmeter of measuring accuracy in the present large diameter pipeline, adopt other flowmeter can't reach the requirement of accuracy calibration.And when ultrasonic flowmeter calibrated, adopt electromagnetic flowmeter as standard scale it to be calibrated, although satisfied the accuracy calibration requirement, the expense of heavy caliber electromagnetic flowmeter is to be higher than ultrasonic flowmeter itself far away.

In sum, there are the following problems for the method for existing calibration heavy caliber flowing meter:

(1) to electromagnetic flowmeter, adopt ultrasonic flowmeter to its calibration of comparing, because the precision of ultrasonic flowmeter is lower than the precision of electromagnetic flowmeter, therefore normally the precision of electromagnetic flowmeter is down to the rank that can make the ultrasonic flow meter calibrating automatically, but this calibrating mode is owing to the precision that has reduced flowmeter integral body, so calibration result can not be revised the test result of electromagnetic flowmeter accurately.

(2) to ultrasonic flowmeter, adopt the high electromagnetic flowmeter of precision to its calibration of comparing, increased a large amount of expenses and paid, and expense ultrasonic flowmeter head and shoulders above itself.

Summary of the invention

The objective of the invention is provides a kind of method of heavy caliber flowing meter on-line calibration for solving the above-mentioned problems in the prior art, and the method is novel, and calibration accurately.

Design philosophy of the present invention: because the precision of turbo flow meter is the highest in the existing flowmeter, can reach 0.2%, therefore for improving calibration accuracy, adopt turbo flow meter as standard scale, but the range of this flowmeter limits to some extent, institute's measurement of discharge is 1000m to the maximum ³/ h, and the flow of large diameter pipeline is generally (2000～6000) m ³Therefore/h introduces the thought of by-pass shunt, makes flow value in the bypass duct within turbo flow meter institute survey scope.By the measurement result of bypass duct flow and the funtcional relationship between the total pipeline flowmeter, can realize the on-line calibration to heavy caliber flowing meter.

Technical solution of the present invention: based on the calibrating principle of method of standard table, adopt the higher turbo flow meter of precision as the calibration of standard scale realization to heavy caliber flowing meter; Consideration based on the turbo flow meter range, upstream or downstream (particular location is looked on-the-spot actual conditions and decided) at heavy caliber flowing meter are drawn a bypass duct, resettlement standard flowmeter in pipeline, then when fluid process flowmeter, the flow number of record standard flowmeter, measurement result and the relation of the mathematical function between the total pipeline heavy caliber flowing meter according to the bypass duct flow realize the calibration to heavy caliber flowing meter.

Described bypass calibration method is a kind of method of heavy caliber flowing meter on-line calibration, and the concrete steps of the method are as follows:

Step 1: the selection of proving flowmeter

In the heavy caliber flowing meter, for the highest, can reach 0.2～0.5% with the precision of electromagnetic flowmeter, for satisfying the requirement of accuracy calibration, to adopt precision be 0.2% turbo flow meter realizes on-line calibration to heavy caliber flowing meter as proving flowmeter.

Step 2: the design of bypass duct

Draw total pipeline and bypass duct figure.Figure 2 shows that total pipeline and bypass duct design diagram, turbo flow meter is positioned over the centre position of branch road, Q among the figure ₀The flow of total pipeline between expression A point and the B point; L ₀The length of total pipeline between expression A point and the B point; D ₀The caliber of expression total pipeline; Q _xThe flow of expression bypass duct; L ₁The length of expression turbo flow meter upstream line; L ₃The length of expression turbo flow meter downstream line; D ₁, D ₃The caliber of expression bypass duct; D ₂The inside nominal diameter of expression turbo flow meter; L ₂The pipe laying length of expression turbo flow meter.

Total stream energy equation in formula (1) the expression fluid mechanics, subscript 1,2 represents section A and B, z in the formula ₁, z ₂The potential energy of expression fluid, p ₁, p ₂The pressure of expression section A and B, g represents acceleration of gravity, general value 9.8m/s ², ρ represents the density of fluid, V ₁, V ₂The expression fluid is at the mean flow rate at section A and B place, α ₁, α ₂Expression kinetic energy correction factor, general value is 0.1, h in the uniform situation of velocity flow profile _wThe expression loss of flood peak.Because each branch road is identical at split point A with pressure difference between the point B, can get formula (2) is that the loss of flood peak is identical.

$z_1+\frac{p_1}{\mathrm{g\ρ}}+\frac{{\mathrm{\α}}_1{V}_1^2}{2g}=z_2+\frac{p_2}{\mathrm{g\ρ}}+\frac{{\mathrm{\α}}_2{V}_2^2}{2g}+h_w---\left(1\right)$

h _f1+h _f2+h _f3＝h _f0 (2)

With formula

Thank to neat coefficient

And Manning formula

Substitution formula (2), wherein λ is retardation factor, n is the coefficient of roughness, relevant with protrusion, the degree of roughness of tube wall, suppose that bypass duct and total pipeline adopt same material, then the n value is identical, can draw the relational expression (3) between flow, caliber and the flow process three of total pipeline and bypass duct.

$\frac{L_1{Q_x}^2}{D_1^{16/3}}+\frac{L_2{Q_x}^2}{D_2^{16/3}}+\frac{L_3{Q_x}^2}{D_3^{16/3}}=\frac{L_0{Q_0}^2}{D_0^{16/3}}---\left(3\right)$

Set $\left\{\begin{array}{c}{L}_1=L_3={\mathrm{aL}}_2\\ D_1=D_3={\mathrm{bD}}_2\end{array}\right.,$ A, b represent scale-up factor in the formula, and substitution formula (3) draws:

$(2\mathrm{\δ}-\frac{2}{b^{16/3}})a=1-\mathrm{\δ}---\left(4\right)$

Wherein If make the bypass duct size design reach minimum, namely the value of a and b is minimum, then should choose maximum δ value.

For trying to achieve the physical dimension of bypass duct, consider following some: (1) chooses the turbo flow meter of respective model according to the difference of the actual test environment in scene, can obtain parameter D ₂Size; (2) in conjunction with actual conditions, the value of a and b all should be greater than 0; (3) turbo flow meter requires the upstream and downstream side that the straight length that is no less than 20DN and 5DN with the length of the identical inside nominal diameter of sensor should be arranged respectively when installing and using.

In above three condition substitution formula (4), can draw the physical dimension of bypass duct.

Step 3: the installation of standard scale

After the size of determining turbo flow meter model and bypass duct, turbo flow meter is mounted in the bypass duct, should guarantee in the installation process that the flowmeter axis should be concentric with conduit axis, flow to consistent, and guarantee the smooth cleaning of inner-walls of duct, without the time defective such as obvious indenture, incrustation and peeling, when containing impurity in the fluid, should add fixed filter, guarantee turbo flow meter measuring accuracy in use.

Step 4: method Performance Evaluation

By on theoretical modeling and the basis that simulation analysis combines, tentatively set up the funtcional relationship between bypass duct flow and house steward's flow, then carry out a large amount of actual measurement work, perform statistics and the record of parameters, by the theoretical model of setting up of the modified result of reality test, to guarantee that this method of testing accuracy requirement and realization are to the on-line calibration of heavy caliber flowing meter.

The present invention's advantage compared with prior art is: the turbo flow meter that precision is the highest in the employing current flux meter among the present invention is as the on-line calibration of standard scale realization to heavy caliber flowing meter, its precision can reach 0.2%, satisfy the calibration accuracy requirement, and the thought of introducing by-pass shunt guaranteed the work range ability of turbo flow meter, improved on the whole the calibration accuracy to flowmeter.

Description of drawings

Fig. 1 is method of standard table on-line calibration system chart.

Fig. 2 is the bypass duct design diagram.

Fig. 3 is FB(flow block) of the present invention.

Symbol description is as follows among Fig. 2:

A, B represent respectively section; Q ₀The flow of total pipeline between expression A point and the B point; L ₀The length of total pipeline between expression A point and the B point; D ₀The caliber of expression total pipeline; Q _xThe flow of expression bypass duct; L ₁The length of expression turbo flow meter upstream line; L ₃The length of expression turbo flow meter downstream line; D ₁, D ₃The caliber of expression bypass duct; D ₂The inside nominal diameter of expression turbo flow meter; L ₂The pipe laying length of expression turbo flow meter.

Embodiment

Figure 1 shows that method of standard table on-line calibration system chart, draw a bypass duct, resettlement standard flowmeter in bypass duct in the flowmeter downstream that total pipeline is installed.Proving flowmeter adopts the highest turbo flow meter of present precision, and its precision can reach 0.2%, is higher than the precision 0.5% of electromagnetic flowmeter in the present heavy caliber flowing meter.Flow through by shunt conduit by the flowmeter in the total pipeline when fluid the bypass duct of turbo flow meter is installed, the flow indicating value of two kinds of flowmeters of record, draw funtcional relationship between the two through theoretical model, further to reach the purpose of calibration heavy caliber flowing meter.

See Fig. 3, the method for a kind of heavy caliber flowing meter on-line calibration of the present invention, the concrete steps of the method are as follows:

Step 1: the selection of proving flowmeter

In the heavy caliber flowing meter, for the highest, can reach 0.2～0.5% with the precision of electromagnetic flowmeter, for satisfying the requirement of accuracy calibration, to adopt precision be 0.2% turbo flow meter realizes on-line calibration to heavy caliber flowing meter as proving flowmeter.

Step 2: the design of bypass duct

Draw total pipeline and bypass duct figure.Figure 2 shows that total pipeline and bypass duct design diagram, turbo flow meter is positioned over the centre position of branch road, Q among the figure ₀The flow of total pipeline between expression A point and the B point; L ₀The length of total pipeline between expression A point and the B point; D ₀The caliber of expression total pipeline; Q _xThe flow of expression bypass duct; L ₁The length of expression turbo flow meter upstream line; L ₃The length of expression turbo flow meter downstream line; D ₁, D ₃The caliber of expression bypass duct; D ₂The inside nominal diameter of expression turbo flow meter; L ₂The pipe laying length of expression turbo flow meter.

Total stream energy equation in formula (1) the expression fluid mechanics, subscript 1,2 represents section A and B, z in the formula ₁, z ₂The potential energy of expression fluid, p ₁, p ₂The pressure of expression section A and B, h _wThe expression loss of flood peak.Because each branch road is identical at split point A with pressure difference between the point B, can get formula (2) is that the loss of flood peak is identical.

$z_1+\frac{p_1}{\mathrm{g\ρ}}+\frac{{\mathrm{\α}}_1{V}_1^2}{2g}=z_2+\frac{p_2}{\mathrm{g\ρ}}+\frac{{\mathrm{\α}}_2{V}_2^2}{2g}+h_w---\left(1\right)$

h _f1+h _f2+h _f3＝h _f0 (2)

With formula

Thank to neat coefficient

And Manning formula

Substitution formula (2), wherein λ is retardation factor, can draw the relational expression (3) between flow, caliber and the flow process three of total pipeline and bypass duct.

$\frac{L_1{Q_x}^2}{D_1^{16/3}}+\frac{L_2{Q_x}^2}{D_2^{16/3}}+\frac{L_3{Q_x}^2}{D_3^{16/3}}=\frac{L_0{Q_0}^2}{D_0^{16/3}}---\left(3\right)$

Set $\left\{\begin{array}{c}{L}_1=L_3={\mathrm{aL}}_2\\ D_1=D_3={\mathrm{bD}}_2\end{array}\right.,$ And substitution formula (3), draw:

$(2\mathrm{\δ}-\frac{2}{b^{16/3}})a=1-\mathrm{\δ}---\left(4\right)$

Wherein

If make the bypass duct size design reach minimum, namely the value of a and b is minimum, then should choose maximum δ value.

For trying to achieve the physical dimension of bypass duct, consider following some: (1) chooses the turbo flow meter of respective model according to the difference of the actual test environment in scene, can obtain parameter D ₂Size; (2) in conjunction with actual conditions, the value of a and b all should be greater than 0; (3) turbo flow meter requires the upstream and downstream side that the straight length that is no less than 20DN and 5DN with the length of the identical inside nominal diameter of sensor should be arranged respectively when installing and using.

In above three condition substitution formula (4), can draw the physical dimension of bypass duct.

Step 3: the installation of standard scale

After the size of determining turbo flow meter model and bypass duct, turbo flow meter is mounted in the bypass duct, should guarantee in the installation process that the flowmeter axis should be concentric with conduit axis, flow to consistent, and guarantee the smooth cleaning of inner-walls of duct, without defectives such as obvious indenture, incrustation and peelings, when containing impurity in the fluid, should add fixed filter, guarantee turbo flow meter measuring accuracy in use.

Step 4: method Performance Evaluation

By on theoretical modeling and the basis that simulation analysis combines, tentatively set up the funtcional relationship between bypass duct flow and house steward's flow, then carry out a large amount of actual measurement work, perform statistics and the meter record of parameters, by the theoretical model of setting up of the modified result of reality test, to guarantee that this method of testing accuracy requirement and realization are to the on-line calibration of heavy caliber flowing meter.

Figure 3 shows that FB(flow block) of the present invention, at first select the high flowmeter of a kind of precision as standard scale, to satisfy the accuracy calibration requirement of heavy caliber flowing meter, then go out the physical dimension of bypass duct according to hydromechanical energy equation reasoning and calculation, on this basis, standard scale is installed in the bypass duct that designs, the mode analysis that combines with experiment by theory at last draws the funtcional relationship between bypass duct flow and total pipeline flow, to guarantee that this method of testing accuracy requirement and realization are to the on-line calibration of heavy caliber flowing meter.

Claims (1)

1. the method for a heavy caliber flowing meter on-line calibration, it is characterized in that: the concrete steps of the method are as follows:

Step 1: the selection of proving flowmeter

In the heavy caliber flowing meter, for the highest, reach 0.2～0.5% with the precision of electromagnetic flowmeter, for satisfying the requirement of accuracy calibration, to adopt precision be 0.2% turbo flow meter realizes on-line calibration to heavy caliber flowing meter as proving flowmeter;

Step 2: the design of bypass duct

Draw total pipeline and bypass duct figure, turbo flow meter is positioned over the centre position that bypass duct is branch road, Q ₀The flow of total pipeline between expression A point and the B point, L ₀The length of total pipeline between expression A point and the B point, D ₀The caliber of expression total pipeline, Q _xThe flow of expression bypass duct, L ₁The length of expression turbo flow meter upstream line, L ₃The length of expression turbo flow meter downstream line, D ₁, D ₃The caliber of expression upstream line, downstream tube, D ₂The inside nominal diameter of expression turbo flow meter, L ₂The pipe laying length of expression turbo flow meter;

Total stream energy equation in formula (1) the expression fluid mechanics, subscript 1,2 represents section A and B, z in the formula ₁, z ₂The potential energy of expression fluid, p ₁, p ₂The pressure of expression section A and B, g represents acceleration of gravity, general value 9.8m/s ², ρ represents the density of fluid, V ₁, V ₂The expression fluid is at the mean flow rate at section A and B place, α ₁, α ₂Expression kinetic energy correction factor, value is 0.1, h in the uniform situation of velocity flow profile _wThe expression loss of flood peak; Because each branch road is identical at split point A with pressure difference between the point B, getting formula (2) is loss of flood peak identical relation;

$z_1+\frac{p_1}{\mathrm{g\ρ}}+\frac{{\mathrm{\α}}_1{V_1}^2}{2g}=z_2+\frac{p_2}{\mathrm{g\ρ}}+\frac{{\mathrm{\α}}_2{V_2}^2}{2g}+h_w---\left(1\right)$

h _f1+h _f2+h _f3=h _f0 （2）

With formula Thank to neat coefficient And Manning formula

Substitution formula (2), wherein λ is retardation factor, and n is the coefficient of roughness, and is relevant with protrusion, the degree of roughness of tube wall, supposes that bypass duct and total pipeline adopt same material, and then the n value is identical, draws relational expression (3)

$\frac{L_1{Q_x}^2}{{D_1}^{16/3}}+\frac{L_2{Q_x}^2}{{D_2}^{16/3}}+\frac{L_3{Q_x}^2}{{D_3}^{16/3}}=\frac{L_0{Q_0}^2}{{D_0}^{16/3}}---\left(3\right)$

Set $\left\{\begin{array}{c}{L}_1=L_3=a{L}_2\\ D_1=D_3=b{D}_2\end{array}\right.,$ A, b represent scale-up factor in the formula, and substitution formula (3) draws:

$(2\mathrm{\δ}-\frac{2}{b^{16/3}})a=1-\mathrm{\δ}---\left(4\right)$

Wherein

If make the bypass duct size design reach minimum, namely the value of a and b is minimum, then should choose maximum δ value;

For trying to achieve the physical dimension of bypass duct, consider following some: (1) chooses the turbo flow meter of respective model according to the difference of the actual test environment in scene, obtains the size of the inside nominal diameter of turbo flow meter; (2) in conjunction with actual conditions, the value of a and b all should be greater than 0; (3) turbo flow meter requires the upstream and downstream side that the straight length that is no less than 20DN and 5DN with the length of the identical inside nominal diameter of turbo flow meter should be arranged respectively when installing and using;

In above three condition substitution formula (4), namely draw the physical dimension of bypass duct;

Step 3: the installation of turbo flow meter

After the size of determining turbo flow meter model and bypass duct, turbo flow meter is mounted in the bypass duct, should guarantee in the installation process that the flowmeter axis should be concentric with conduit axis, flow to consistent, and guarantee the smooth cleaning of inner-walls of duct, without obvious indenture, incrustation and peeling defective, when containing impurity in the fluid, should add fixed filter, guarantee turbo flow meter measuring accuracy in use;

Step 4: method Performance Evaluation

By on theoretical modeling and the basis that simulation analysis combines, tentatively set up the funtcional relationship between bypass duct flow and total pipeline flow, then carry out a large amount of actual measurement work, perform statistics and the record of parameters, by the theoretical model of setting up of the modified result of reality test, to guarantee that this method of testing accuracy requirement and realization are to the on-line calibration of heavy caliber flowing meter.

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